Semiconductor light-emitting element and light-emitting device

ABSTRACT

A semiconductor light-emitting element has a laminated section which has an active layer made of a semiconductor, and first and second clad layers each being disposed to sandwich the active layer and made of a semiconductor, a pair of first high-reflection layers each being disposed to sandwich the active layer in a first direction orthogonal to the laminated direction of the laminated section, and a low-reflection layer and a second high-reflection layer each being disposed to sandwich the active layer in a second direction orthogonal to the laminated direction and crossing to the first direction.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application N0. 2005-36573, filed on Feb. 14,2005, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light-emitting element and alight-emitting device and, particularly, to a semiconductorlight-emitting element and a light-emitting device in which asemiconductor material is used.

2. Related Art

Semiconductor light-emitting elements are widely used in displaydevices, lighting devices, recording devices, etc. Particularly,semiconductor light-emitting diodes (LEDs) which do not use stimulatedemission are used as display devices because of their high luminance. Asa recent new application, trials have been made to use an LED as alighting device in which an LED and a fluorescent material layer arecombined (refer to the Japanese Patent Laid-Open No. 2004-179644, forexample). This publication discloses a fluorescent-material laminatedstructure in which two kinds of fluorescent material layers arelaminated on a semiconductor light-emitting element such as an LED, inorder to increase color rendering properties, and a light-emittingdevice of white color etc. in which this fluorescent-material laminatedstructure is used. In the fluorescent material layers of thislight-emitting device, a diffusion agent, a binder resin and afluorescent material are blended by being adjusted. This increasesluminous efficiency and suppresses the deterioration of the fluorescentmaterial layers.

In the conventional light-emitting device described in the above-citedpublication, the lighting device in which an LED and fluorescentmaterial layers are combined intends to improve the luminance of thelighting device by contriving the material and structure of thefluorescent material layers. However, the conventional technique issufficient for use in a lighting device. That reason will be describedbelow.

LEDs are excellent in high efficiency and small heat generation,compared to the existing electric lamps. Therefore, it is assumed thatthe existing electric lamps will be more and more replaced in the futureby combinations of an LED and a high-luminance fluorescent materiallayer. On the other hand, compared to fluorescent lamps which are widelyused as lighting devices, LEDs have still problems in efficiency, heatgeneration and operating power source, and even when high-luminancefluorescent material layers are used, it will be practically difficultto obtain an excellent luminous efficiency (luminous efficiency relativeto input power) enough to replace the fluorescent lamps. Thus,conventional LEDs have the problem that they are not sufficient in termsof efficiency, heat generation and operating power source and that it isdifficult to obtain an excellent luminous efficiency enough to replacethe fluorescent lamps which are widely used as lighting devices.

SUMMARY OF THE INVENTION

In order to solve the above-described problem, an object of the presentinvention is to provide a semiconductor light-emitting element and alight-emitting device having a high light-emitting efficiency relativeto an input power.

According to one embodiment of the present invention, a semiconductorlight-emitting element, comprising:

a laminated section which has an active layer made of a semiconductor,and first and second clad layers each being disposed to sandwich theactive layer and made of a semiconductor;

a pair of first high-reflection layers each being disposed to sandwichthe active layer in a first direction orthogonal to the laminateddirection of the laminated section, which have high reflectance relativeto a light emitted by the active layer; and

a low-reflection layer and a second high-reflection layer each beingdisposed to sandwich the active layer in a second direction orthogonalto the laminated direction and crossing to the first direction, whichhave low reflectance and high reflectance respectively relative to thelight emitted by the active layer.

Furthermore, according to one embodiment of the present invention, alight-emitting device, comprising:

a mount substrate which has a heat sink; and

a semiconductor light-emitting element mounted on the heat sink,

wherein the semiconductor light-emitting element has:

a laminated section which has an active layer made of a semiconductor,and first and second clad layers each being disposed to sandwich theactive layer and made of a semiconductor;

a pair of first high-reflection layers each being disposed to sandwichthe active layer in a first direction orthogonal to the laminateddirection of the laminated section, which have high reflectance relativeto a light emitted by the active layer; and

a second high-reflection layer each being disposed to sandwich theactive layer in a second direction orthogonal to the laminated directionand crossing to the first direction, which have low reflectance and highreflectance respectively relative to the light emitted by the activelayer,

the laminated direction of the laminated section being disposed inparallel to a surface on which the semiconductor light-emitting elementon the heat sink is disposed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view which shows a structure of a semiconductorlight-emitting element according to the first embodiment of the presentinvention.

FIG. 2A is a side view as viewed from the n-side electrode 101 side, andFIG. 2B is a side view as viewed from the p-side electrode 102 side.

FIG. 3A-3H are perspective views which shows a method of manufacturing asemiconductor light-emitting element of this embodiment.

FIG. 4 is a sectional view which shows a structure of a light-emittingdevice related to the second embodiment of the present invention.

FIGS. 5A and 5B are diagrams which show the refractive-indexdistribution of this n-type clad layer.

FIG. 6 is a perspective view which shows a structure of a semiconductorlight-emitting element related to this embodiment.

FIG. 7 is a perspective view which shows an example in which thesemiconductor light-emitting element of FIG. 1 is mounted on a printedcircuit board.

FIG. 8 is a diagram in which a light guiding plate is disposed around anactive layer.

FIG. 9 is a diagram showing an example in which a reflection plate or adiffusion plate is disposed along an emitting direction of asemiconductor light-emitting element.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the drawings.

First Embodiment

FIG. 1 is a perspective view which shows a structure of a semiconductorlight-emitting element according to the first embodiment of the presentinvention. The semiconductor light-emitting element shown in FIG. 1 isprovided with a GaN-based compound semiconductor chip in a rectangularshape. This chip has a structure which is obtained by laminating ap-type GaN contact layer 103 doped with Mg, a p-type Al_(0.05)Ga_(0.95)Nclad layer 104 doped with Mg, a p-type Al_(0.2)Ga_(0.8)N overflowpreventing layer 105 doped with Mg, a GaN guide layer 106 which is notdoped, an active layer 107 having a multi-quantum well structure inwhich a well layer is In_(0.2)Ga_(0.8)N and a barrier layer isIn_(0.03)Ga_(0.97)N, an n-type GaN guide layer 108 doped with Si, ann-type Al_(0.05)Ga_(0.95)N clad layer 109 doped with Si, and an n-typeGaN contact layer 110 doped with Si in this order.

A p-side electrode 102 is connected to the p-type GaN contact layer 103,and an n-side electrode 101 is connected to the n-type GaN contact layer110. The p-side electrode 102 is disposed along two surfaces of thechip, and the n-side electrode 101 is also disposed along two surfacesof the chip. As indicated by solid lines, the n-side electrode 101 onthe surface A side has the shape of a rectangle. A comb shape indicatedby dotted lines within the n-side electrode 101 will be described later.

Multiple surfaces of the GaN-based compound semiconductor chip shown inFIG. 1 (the four surfaces A, B, C and D except the surface on which then-side electrode 101 is provided and the surface on which the p-sideelectrode 102 is provided) are provided with either a high-reflectionlayer or a low-reflection layer. FIG. 2A is a side view as viewed fromthe n-side electrode 101 side (from the direction E), and FIG. 2B is aside view as viewed from the p-side electrode 102 side (from thedirection F).

As shown in FIG. 2A, the surface of the GaN-based compound semiconductorchip on the side A is provided with a low-reflection layer 203, and thesurface thereof on the side B is provided with a high-reflection layer202. Also, the surface on the side C and the surface on the side D arerespectively provided with high-reflection layers 201 b, 201 a. Thesehigh-reflection layers 201 b, 201 a, 202 and low-reflection layer 203are omitted in FIG. 1.

The low-reflection layer 203 is formed of a dielectric multilayer filmor the like and for example, SiO₂, SiN, Al₂O₃, etc. can be used. Thereflectance of the low-reflection layer 203 in this embodiment is, forexample, 10%. The high-reflection layers 201 b, 201 a, 202 are formed ofa dielectric multilayer film or the like, and for example, a laminatedfilm in which TiO₂/SiO₂ is repeatedly formed or the like can be used.The film thickness of TiO₂ and SiO₂ is a thickness corresponding to ¼ ofa central wavelength of the light-emitting layer (the active layer 107).Although the number of repetitions can be, for example, 10 pairs in all,it is not limited to this figure. In this embodiment, the reflectance ofthe high-reflection layers is, for example, 99%.

The above-described high-reflection layers 201 a, 201 b are disposed onboth end surfaces in the first direction (the direction which connects Cand D) orthogonal to the lamination direction of a laminated sectionwhich has the active layer 107, the n-type Al_(0.05)Ga_(0.95)N cladlayer 109 and the p-type Al_(0.05)Ga_(0.95)N clad layer 104, and have ahigh reflectance relative to the light generated in the active layer107.

The above-described low-reflection layer 203 and high-reflection layer202 are provided on both end surfaces by sandwiching the active layer107 in the second direction (the direction which connects A and B) whichis orthogonal to the above-described lamination direction and intersectsthe first direction, and have a low reflectance and a high reflectancerelative to the light generated in the active layer 107, respectively.

When a current flow through the semiconductor light-emitting element ofFIG. 1, a waveguide structure is formed by the n-typeAl_(0.05)Ga_(0.95)N clad layer 109 and the p-type Al_(0.05)Ga_(0.95)Nclad layer 104, and the light can be trapped in the active layer 107. Atthe same time, the light is caused to resonate by the pair ofhigh-reflection layers 201 a, 201 b each having a high reflectance.Because the active layer 107 has a gain, it is possible to suppress theabsorption of light caused when the light emitted by the active layer107 crosses again the active layer 107 due to internal reflection(multiple reflection).

Because the low-reflection layer 203 and the high-reflection layer 202are provided so that light can be taken out in a direction whichintersects the direction of oscillation, it is possible to increase theluminous efficiency of the element twice or so by taking out the lightemitted in the active layer 107 to the outside via the low-reflectionlayer 203.

Also, the semiconductor light-emitting element according to the presentembodiment has an element shape of which the length in a directionperpendicular to both the above-described lamination direction and thesecond direction (the direction which connects A and B), in other words,the length in the depth direction of FIG. 1, i.e., the first direction,is larger than the length in the direction perpendicular to both thislamination direction and the first direction (the direction whichconnects C and D), in other words, the length in the vertical directionof FIG. 1, i.e., the second length. In the case of this element shape,the sectional area of the active layer 107 on a surface perpendicular tothe second direction is larger than the sectional area of the activelayer 107 on a surface perpendicular to the first direction. Therefore,the area of the light-emitting region in the light-radiating directionof the element becomes large compared to the sectional areaperpendicular to the radiating direction. Furthermore, theabove-described length in the first direction is larger than theabove-described length in the second direction. Therefore, even in acase where the reflectance is not sufficient, an oscillation thresholdcurrent is reduced and the luminous efficiency relative to input powercan be improved.

Furthermore, in an ordinary laser, it is necessary to provide a regionin which a wire is connected to an n-side electrode and a p-sideelectrode and only a limited part of an element becomes a light-emittingregion. According to the semiconductor light-emitting element of thepresent embodiment, it is possible to make the light-emitting regionoccupied in the element much larger and the element chip can beeffectively used. Therefore, it is possible to increase the number ofelements obtained from one wafer by 20 times or so.

By ensuring that the reflectance of the high-reflection layers 201 a,201 b relative to the light generated in the active layer 107 is notless than 80%, preferably not less than 95%, the oscillation thresholdcurrent is reduced and the luminous efficiency relative to input powercan be improved. Furthermore, by ensuring that the reflectance of thelow-reflection layer 203 relative to the light generated in the activelayer 107 is not more than 10%, the light takeout efficiency can beimproved and the luminous efficiency relative to input power can beimproved.

Because the n-side electrode 101 which supplies current to the activelayer 107 is in contact with a surface parallel to the laminationdirection of the above-described laminated section of the n-type GaNcontact layer 110 (the face A), it is possible to ensure a wide contactarea on this parallel surface. As a result of this, the contactresistance at the metal semiconductor interface can be reduced and theoperating voltage of the element can also be reduced.

When the p-side electrode 102 is in contact with a surface parallel tothe lamination direction of the above-described laminated section of thep-type GaN contact layer 103 (the surface B), similarly the operatingvoltage can be reduced. Because in this embodiment, the element has alength in the lamination direction longer than lengths in the first andsecond directions, it becomes very easy to obtain a wide contact area.

Furthermore, in the semiconductor light-emitting element of thisembodiment, the n-side electrode 101 and the p-side electrode 102 are incontact with the element over a wide area compared to an ordinary edgeemitting type laser. Therefore, heat dissipating properties are good andcurrent density can be increased.

Next, a method of manufacturing a semiconductor light-emitting elementaccording to this embodiment will be described below. FIG. 3 is aperspective view which shows a method of manufacturing a semiconductorlight-emitting element of this embodiment.

First, an n-type GaN substrate is disposed in a crystal growth device.This n-type GaN substrate functions as an n-type GaN contact layer 110doped with Si. By performing crystal growth which uses the MOCVDprocess, upon this n-type GaN substrate are formed an n-typeAl_(0.05)Ga_(0.95)N clad layer 109 doped with Si, an n-type GaN guidelayer 108 doped with Si, an active layer 107 having a multi-quantum wellstructure in which a well layer is In_(0.2)Ga_(0.8)N and a barrier layeris In_(0.03)Ga_(0.97)N, a GaN guide layer 106 which is not doped, ap-type Al_(0.2)Ga_(0.8)N overflow preventing layer 105 doped with Mg, ap-type Al_(0.05)Ga_(0.95)N clad layer 104 doped with Mg, and a p-typeGaN contact layer 103 doped with Mg in this order.

Next, the n-type GaN substrate for which such crystal growth has beenperformed is taken out of the crystal growth device and as shown in FIG.3A, an SiO₂ film 401 is laminated on the p-type GaN contact layer 103.

Next, a resist pattern is formed on the surface of the SiO₂ film 401,and by patterning the SiO₂ film 401 using this resist pattern, openingsformed from rectangles of 5 μm×80 μm are provided lengthwise andcrosswise in rows on the SiO₂ film 401. The pitch of the multipleopenings which are adjacent to each other in the longitudinal directionof the openings is 100 μm and the pitch of the multiple openings whichare adjacent to each other in the direction of the short side is 10 μm.Ammonium fluoride is used to remove the SiO₂ film 401.

Next, as shown in FIG. 3B, scribe lines are marked along a directionthat the openings are disposed on the surface of the n-type GaNsubstrate. For example, the <11-20> direction is used as the cleavagedirection. The scribe lines are marked while observing the surface ofthe p-type GaN contact layer 103 so that cleavage is formed to avoid theopenings on the P-type GaN contact layer 103. The n-type GaN substrateis cleaved along a cleavage plane, with the scribe line serving as thestarting point, and separated into multiple bar-like bodies 402. Thewidth of the bar-like body 402 along the short side (the width along thelongitudinal direction of the openings) is 100 μm.

Next, as shown in FIG. 3C, in this state, a dielectric multilayer film403 is evaporated on the cleavage plane as high-reflection layers 201 b,201 a. The dielectric multilayer film 403 is laminated in quantities of10 pairs in all by repeating TiO₂/SiO₂. The reflectance of thisdielectric multilayer film 403 is not less than 99% relative to emissionwavelength. During the evaporation of the dielectric multilayer film403, the film thickness of each layer is adjusted so that it becomes athickness corresponding to ¼ of the central wavelength of thelight-emitting layer (the active layer 107). This evaporation isperformed for cleavage planes of the bar-like body 402 on both sides.

Next, as shown in FIG. 3D, one element chip 404 is fabricated byperforming the breaking of the bar-like body 402 in the crosswisedirection. This breaking is performed while observing the surface of theP-type GaN contact layer 103 so that cleavage is formed to avoid theopenings on the p-type GaN contact layer 103. The width of the elementchips 404 (the width along the crosswise direction of the opening) is 10μm.

By fabricating the element chips 404 by cleavage in this manner, thevolume per element can be reduced, and each wafer can be effectivelyused, with the result that a yield improvement and a cost reduction canbe achieved.

Next, in this state, the element chips 404 are arrayed and fixed on asupport substrate or a support bed so that the lamination directionbecomes horizontal. Furthermore, as shown in FIG. 3E, upon a cleavageplane on one side is evaporated a dielectric multilayer film 405 as ahigh-reflection layer 202. The dielectric multilayer film 405 islaminated in quantities of 10 pairs in all by repeating TiO₂/SiO₂. Thereflectance of this dielectric multilayer film 405 is not less than 99%relative to emission wavelength. During the evaporation of thedielectric multilayer film 405, the film thickness of each layer isadjusted so that it becomes a thickness corresponding to ¼ of thecentral wavelength of the light-emitting layer (the active layer 107).

Next, as shown in FIG. 3F, a metal film 406 as a p-side electrode 102 isevaporated from the openings on the p-type GaN contact layer 103 to thesurface where the dielectric multilayer film 405 has been formed. Inorder to increase the area of contact between the p-side electrode 102and the p-type GaN contact layer 103, it is also possible to provideopenings on the surface of the p-type GaN contact layer 103 where thedielectric multilayer film 405 has been formed and to form the metalfilm 406 so as to bury the openings. The metal film 406 is patterned asrequired.

Next, as shown in FIG. 3G, the element chips 404 are moved onto anothersupport substrate or a support bed, and the element chips 404 arearrayed and fixed so that the side where the dielectric multilayer film405 has been laminated comes into contact with the support substrate orthe support bed. Furthermore, as shown in FIG. 3G, a dielectric film 407is evaporated as a low-reflection layer 203 on a cleavage plane on theopposite side. For example, SiO₂ is laminated as the dielectric film407. The reflectance of this dielectric film 407 is not more than 10%relative to emission wavelength. During the evaporation of thedielectric film 407, the film thickness is adjusted so that it becomes athickness corresponding to ½ of the central wavelength of thelight-emitting layer (the active layer 107).

After that, an opening is formed on the surface of the n-type GaNcontact layer 110 where the dielectric film 407 has been formed (thesurface parallel to the lamination direction of crystal growth).Ammonium fluoride is used to remove the dielectric film (SiO₂ film) 407.Next, as shown in FIG. 3H, a metal film 408 as an n-side electrode 101is buried in the opening which exposes the n-type GaN contact layer 110,and at the same time, the metal film 408 is evaporated over to a surfaceadjacent to the surface where this opening is provided (the surfaceparallel to the lamination direction of crystal growth), i.e., thesurface perpendicular to the lamination direction of crystal growth. Arelatively large opening can be provided in the surface of the n-typeGaN contact layer 110 where the dielectric film 407 has been formed (thesurface parallel to the lamination direction of crystal growth) and itis possible to increase the area of contact between the n-side electrode101 and the n-type GaN contact layer 110.

Next, in order to prevent the active layer 107 from being covered withthe metal film 408, the metal film 408 is patterned. For example, thelift-off process is used as a patterning method. A resist pattern isformed on a region including the active layer 107 etc. and this resistpattern is removed with an organic solvent or the like after theevaporation of the metal film 408, whereby the patterning of the metalfilm 408 can be performed.

As described above, in the first embodiment, the light emitted in theactive layer 107 is reciprocated in the first direction to increase theoptical power, and then the light can be taken out to the outside viathe low-reflection layer 203, whereby luminous efficiency can beimproved. Also, because the sectional area of the active layer in thesecond direction, which is the radiation direction of light, is madelarger than the sectional area of the active layer in the firstdirection which is perpendicular to the radiation direction of light,luminous efficiency can be further improved.

Furthermore, because the n-side electrode 101 comes into surface contactwith the n-type contact layer 110 and also the p-side electrode 102comes into surface contact with the p-type GaN contact layer 103,contact resistance can be reduced and the operating voltage of theelement can be reduced. Also, because the n-side electrode 101 and thep-side electrode 102 come into contact with the element over a widearea, heat dissipating properties are improved and current density canbe increased.

Second Embodiment

FIG. 4 is a sectional view which shows a structure of a light-emittingdevice related to the second embodiment of the present invention. Inthis embodiment, the light-emitting device which has a semiconductorlight-emitting element of FIG. 1 mounted on a heat sink will bedescribed. As indicated by solid lines of FIG. 4, a heat sink 302 isdisposed in a region of the top surface of a vertically mountedsubstrate 301 in contact therewith, and a heat sink 305 is disposed inthe other region of the top surface of the vertically mounted substrate301 via an insulator 304. The heat sinks 302, 305 are formed of aconductor. However, the heat sinks 302, 305 are insulated from eachother.

The semiconductor light-emitting element shown in FIG. 1 is disposed onthe heat sink 302 via a solder 303 so that the surface at a side oflaminating a high-reflection layer (a dielectric multilayer film) 202faces the heat sink 302. The solder 303 is electrically conducted withthe portion of a p-side electrode 102 which extends on the dielectricmultilayer film 202 and heat sink 302.

A solder 306 is formed between an n-side electrode 101 and the heat sink305, and the n-side electrode 101 and the heat sink 305 are electricallyconducted by this solder 306. The n-side electrode 101 and the heat sink305 may be electrically conducted by use of an Au wire in place of thesolder 306. The reference numeral 307 denotes a power source whichapplies a voltage across the heat sink 302 and the heat sink 305, andowing to such a structure, a voltage is applied across the n-sideelectrode 101 and the p-side electrode 102.

With the light-emitting device of the second embodiment, the same effectas described in the first embodiment can be obtained. Besides, heat canbe dissipated from the n-side electrode 101 and p-side electrode 102which are in contact with the element over a wide area into the heatsink 305 and the heat sink 302, respectively via the solder 306 and thesolder 303. Because of this, the temperature characteristics andreliability of the element can be improved by further improving heatdissipating properties and operation at a high output becomes possible.Particularly, it is possible to dispose an active layer 107 of largeheat generation and the p-side electrode 102 near the heat sink 302 andas a result of this, the heat dissipation efficiency can be remarkablyimproved and stable operation at a high output is made possible.

Third Embodiment

The third embodiment relates to a light-emitting device for white lightemission and is an example of a lighting device which replacesfluorescent lamps and the like. A structure of this device will bedescribed by using FIG. 4. As shown in FIG. 4, in the light-emittingdevice of this embodiment, members indicated by dotted line are providedin addition to the structure of the second embodiment (the solid lineportion of FIG. 4). The reference numeral 510 denotes a plastics celland the semiconductor light-emitting element of FIG. 1 is disposedwithin this cell 510. A fluorescent material layer 511 is buried in theinterior of the cell 510 on this semiconductor light-emitting element,and a light takeout window 512 is provided so as to cover thefluorescent material layer 511.

The fluorescent material layer 511 is a layer in which a fluorescentmaterial of red color, a fluorescent material of green color and afluorescent material of blue color are dispersed in a fluorine-basedpolymer. La₂O₂S: Eu, Sm (the elements behind the symbol (:) denoteactivating elements, and the same applies to the following) and the likeare used as a fluorescent material of red color, InGaN, BaMgAl₂₇O₁₇: Eu,Mn and the like are used as a fluorescent material of green color, andInGaN, (Sr, Ca, Ba)₁₀(PO₄)₆Cl₂: Eu and the like are used as afluorescent material of blue color. The fluorescent materials of thesecolors are excited by the light emitted from the semiconductorlight-emitting element and light emission occurs, with the result thatwhite light can be obtained by the superimposing of the light emissionby the fluorescent materials of each color. Incidentally, it is possibleto use a fluorescent material of yellow color in place of a fluorescentmaterial of green color or in combination with a fluorescent material ofgreen color, and for example, (Sr, Ca, Ba)₂SiO₄:Eu and the like areused.

Although the cell 510 is made of a plastics material here, metals,ceramics and glass may also be used. And when metals, ceramics and glassare used, it is possible to obtain a light-emitting device having goodheat dissipating properties and little deteriorates and a high-output,high-reliability light-emitting device can be provided. The fluorescentmaterial layer 511 may be in contact with the semiconductorlight-emitting element, it may be disposed outside the cell 510, or itmay be disposed between the two.

With the light-emitting device of the third embodiment, the same effectsas described in the first and second embodiments can be obtained.Besides, it is possible to obtain a light-emitting device for whitelight emission having excellent rendering properties and high luminousefficiency. Therefore, it is possible to realize a new lighting systemwhich replaces conventional fluorescent lamps.

Fourth Embodiment

The fourth embodiment is such that in the semiconductor light-emittingelement of FIG. 1, a laminated structure of AlGaN/GaN in which thethickness of each layer corresponds to the ¼ wavelength of the emissionwavelength in terms of optical path length is used in place of then-type Al_(0.05)Ga_(0.95)N clad layer 109.

FIGS. 5A and 5B are diagrams which show the refractive-indexdistribution of this n-type clad layer. In the figures, the abscissa isthe position in film thickness direction and the ordinate is therefractive index. As shown in FIG. 5B, the n-type clad layer has alaminated structure in which Al_(0.3)Ga_(0.7)N layers (503, 504) and GaNlayers, which respectively correspond to a thickness of the ¼ wavelengthof the emission wavelength in terms of optical path length, arealternately laminated. Owing to this structure, it is possible to reducethe amount of the light from the active layer 107 which leaks to then-type GaN substrate side (the n-type GaN contact layer 110 side), andluminous efficiency can be improved.

As shown in FIG. 5A, the Al_(0.3)Ga_(0.7)N layers (503, 504) of FIG. 5Bmay be constituted respectively by the superlattices (501, 502) ofAl_(0.65)Ga_(0.35)N and GaN so that the refractive-index distributionhas a double cycle. It is possible to set the thickness ofAl_(0.65)Ga_(0.35)N and GaN at 4.6 rm and 5 mm, respectively.

According to the light-emitting device of the fifth embodiment, the sameeffect as in the first embodiment can be obtained. Besides, in theexample of FIG. 5B, it is possible to increase the optical output duringoperation to about three times as high as in conventional semiconductorlight-emitting elements, although voltage increases. In the example ofFIG. 5A, it is possible to increase the optical output during operationto about three times as high as in conventional semiconductorlight-emitting elements and, at the same time, it is possible to ensurethat operating voltage has similar values as in conventionalsemiconductor light-emitting elements.

The p-type Al_(0.05)Ga_(0.95)N clad layer 104 may have a laminatedstructure in which AlGaN layers and GaN layers, which respectivelycorrespond to a thickness of the ¼ wavelength of the emission wavelengthin terms of optical path length, are alternately laminated. As a resultof this, it is possible to reduce the amount of the light from theactive layer 107 which leaks to the p-type GaN contact layer 103 side,and luminous efficiency can be improved.

Incidentally, only the n-type Al_(0.05)Ga_(0.95)N clad layer 109 mayhave the above-described laminated structure, only the p-typeAl_(0.05)Ga_(0.95)N clad layer 104 may have the above-describedlaminated structure, or both may have the above-described laminatedstructure.

Fifth Embodiment

A fifth embodiment has characteristics in which a film made of anitride-based insulator such as a silicon nitride is provided betweenthe side surfaces of the active layer 107 and the high-reflection layers201 a, 201 b, 202 or the low-reflection layer 203, or the side surfacesof the active layer 107 are subjected to nitriding treatment.

According to the element structure of this embodiment, a nitride-basedinsulator is provided between the active layer 107 and thehigh-reflection layers 201 a, 201 b, 202 and between the active layer107 and low-reflection layer 203 formed on the side surfaces of thisactive layer 107. Therefore, even in a case where a current flows nearthe side surfaces of the active layer 107, surface recombination isreduced owing to the silicon nitride film, making it possible to reducereactive current. Thus, it is possible to improve luminous efficiencyrelative to input power.

Incidentally, a film formed from aluminum nitride and the like may beused in place of silicon nitride. These nitride-based insulators can beformed by CVD and sputtering.

Furthermore, it is preferred that before the formation of a film formedfrom a nitride-based insulator and the high-reflection layers 201 a, 201b, 202 and the low-reflection layer 203 on the active layer 107 side,the side surfaces of the active layer 107 is subjected to nitridingtreatment. This treatment enables a reduction in reactive current and anincrease in luminous efficiency to be further improved. As the nitridingtreatment, it is preferable to adopt a process which involves performingdischarge in a gas such as nitrogen and ammonia, causing a nitrogenradical to be generated by this discharge, and performing surfacetreatment with this nitrogen radical. Incidentally, only nitridingtreatment may also be performed and the side surfaces of the activelayer 107 are not always covered with the above-described nitride-basedinsulator.

Sixth Embodiment

In the semiconductor light-emitting element of a sixth embodiment, ap-type GaN substrate is used in place of the n-type GaN substrate, andthe sixth embodiment is the same as the first embodiment except for thispoint.

FIG. 6 is a perspective view which shows a structure of a semiconductorlight-emitting element related to this embodiment. As shown in FIG. 6,the semiconductor light-emitting element of this embodiment is formedfrom a GaN-based compound semiconductor chip in a rectangular shape.This chip has a structure which is obtained by laminating a p-type GaNcontact layer 603 doped with Mg, a p-type Al_(0.05)Ga_(0.95)N clad layer604 doped with Mg, a p-type Al_(0.2)Ga_(0.8)N overflow preventing layer605 doped with Mg, a GaN guide layer 606 which is not doped, an activelayer 607 having a multi-quantum well structure in which a well layer isIn_(0.2)Ga_(0.8)N and a barrier layer is In_(0.03)Ga_(0.97), an n-typeGaN guide layer 608 doped with Si, an n-type Al_(0.05)Ga_(0.95)N cladlayer 609 doped with Si, and an n-type GaN contact layer 610 doped withSi in this order. A p-side electrode 602 is connected to the p-type GaNcontact layer 603, and an n-side electrode 601 is connected to then-type GaN contact layer 610. An element of such a structure can bemanufactured by the same process as in the first embodiment, with theexception that a p-type GaN substrate is used in place of the n-type GaNsubstrate.

In the element structure of the sixth embodiment, the “p” and “n” of thelayer structure in the first embodiment are interchanged, and the samefunctions and effects as in the first embodiment are obtained. That is,according to this embodiment, it is possible to dramatically increasethe area of contact between the p-type GaN contact layer 603 and thep-side electrode 602, and it is possible to substantially reduce contactresistance in the p-side electrode 602 where contact resistance is aptto increase. As a result of this, the operating voltage can besubstantially reduced and it is possible to dramatically reduce the heatgeneration of the element.

It is also possible to fabricate a light-emitting device shown in FIG. 4by using the semiconductor light-emitting element shown in FIG. 6. Byelectrically connecting the p-side electrode 602 to the heat sink 305via the solder 306 and electrically connecting the n-side electrode 601to the heat sink 302 via the solder 303, it is possible to improve heatdissipation efficiency and to operate the light-emitting device at ahigh output.

It is also possible to electrically connect the p-side electrode 602 tothe heat sink 302 via the solder 303 and to electrically connect then-side electrode 601 to the heat sink 305 via the solder 306. In thiscase, the low-reflection layer 203 is replaced with the high-reflectionlayer 202 so that the n-side electrode 601 does not cover the lightradiation surface of the active layer 607. In this case, the heatdissipation efficiency is further improved and it is possible to operatethe light-emitting device in a stable manner at a high output.

Seventh Embodiment

Although in the above-described third embodiment, an example has beendescribed in which white light is obtained by applying a fluorescentmaterial to the periphery of the semiconductor light-emitting element,the seventh embodiment described below features an application method ofa fluorescent material.

FIG. 7 is a perspective view which shows an example in which thesemiconductor light-emitting element of FIG. 1 is mounted on a printedcircuit board. Upon a printed circuit board 700 are formed an n-sideinterconnection pattern 701 and a p-side interconnection pattern 702which are electrically connected respectively to the n-side electrode101 and p-side electrode 102 of the semiconductor light-emittingelement. These electrodes 101, 102 and interconnection patterns 701, 702are contacted, for example, by a solder 703. Although this is omitted inFIG. 7, a heat sink as shown in FIG. 4 may be connected to thesemiconductor light-emitting element.

Although this is not shown in FIG. 7, with the semiconductorlight-emitting element mounted on the printed circuit board 700, afluorescent material is applied to the whole surface of the substrate.By applying a fluorescent material, the wavelength of the light emittedfrom the semiconductor light-emitting element is changed and white lightcan be obtained.

Usually fluorescent materials have the shape of a particle, and when afluorescent material of this kind is applied to the top surface and sidesurfaces of the semiconductor light-emitting element, the surface colorbecome uneven due to variations in particle size. To prevent thisphenomenon, in this embodiment a fluorescent material is applieddirectly to the periphery of the active layer of the semiconductorlight-emitting element by sputtering. More specifically, a fluorescentmaterial made by an ordinary technique is laminated on the surface ofthe semiconductor light-emitting element where the electrodes are notformed.

As a concrete technique for laminating a fluorescent material, forexample, with the heat sink attached to the semiconductor light-emittingelement, sputtering is performed while rotating the semiconductorlight-emitting element by a planetary system, whereby the fluorescentmaterial is laminated.

More preferably, a fluorescent material is laminated by laser abrasion.As a result of this, a fluorescent material which is free fromvariations in particle size and has a good luminous efficiency can beuniformly formed.

When the light emitted from the element is used as part of white lightby the partial transmission of the light, a fluorescent material layeris formed thin. When a fluorescent material is excited by ultravioletlight, multiple fluorescent material layers are formed as a laminatedstructure. It is also possible to laminate fine crystals on anothercrystal plane in an aqueous solution of zinc chloride or the like. Byusing such techniques, it is possible to obtain good white light freefrom color unevenness.

In a case where a lighting device is to be fabricated by use of thesemiconductor light-emitting element in each of the above-describedembodiments, if the semiconductor light-emitting element is used as itis, then luminance becomes high only in the periphery of the activelayer of the semiconductor light-emitting element and glare occurs.Therefore, as shown in FIG. 8, a light guiding plate 711 may be disposedat the periphery of the active layer so that the density of light isreduced by widening the light-emitting area by this light guiding plate711. Or alternatively, a shown in FIG. 9, the light-emitting area may bewidened by disposing a reflection plate or a diffusion plate 712 alongthe light-emitting direction of the semiconductor light-emitting elementin place of the light guiding plate 711. In the case of FIG. 9, afluorescent material is applied to the reflection plate and thediffusion plate, instead of applying a fluorescent material to thesemiconductor light-emitting element. As a result of this, it ispossible to obtain a good white color while reducing the density oflight.

The present invention is not limited to the above-described embodiments.For instance, in the example of FIG. 3, when fabricating chips of asemiconductor light-emitting element, first, surfaces on which a pair ofhigh-reflection layers are to be formed are fabricated by cleaving thesubstrate and the substrate is separated into multiple bar-like bodies,and then surfaces on which high-reflection layers and a low-reflectionlayer are to be formed are fabricated by cleaving the bar-like bodies,and then the bar-like bodies are separated into multiple element chips.However, this process may be reversed.

That is, it is also possible to adopt the following process. First,scribe lines are formed in the direction corresponding to thelongitudinal direction of the element, whereby surfaces on whichhigh-reflection layers and a low-reflection layer are to be formed arefabricated by cleaving the substrate to separate the substrate intomultiple bar-like bodies. Next, surfaces on which a pair ofhigh-reflection layers is to be formed are fabricated in each of thebar-like bodies by performing cleavage, and then each of the bar-likebodies is separated into multiple element chips. In the formerfabrication process, it is possible to obtain a good efficiency becausecleavage planes can be fabricated at a time. In the latter fabricationprocess, because cleavage planes of the elements are individually formedone after another, accurate cleavage planes are obtained and it ispossible to obtain a good yield.

Although in the example of FIG. 3, the separation of the element isperformed by scribe and cleavage, it may be performed by dry etching. Inthis case, a mask pattern is formed on the substrate surface so that theseparated regions of the substrate are exposed, and the substrate is dryetched by using this mask pattern. When a substrate formed of aGaN-based material is used, it is possible to use metals, such as SiO₂and Mo, and the like as the mask pattern and argon, chlorine, etc. as anetching gas. On that occasion, the shape shown in FIG. 3D can beobtained by performing etching alone and, therefore, it is possible toreduce the frequency of rearrangement and re-bonding of the element canbe reduced.

It is possible to adopt a structure in which the n-side electrode hasthe shape of a comb. For example, in FIG. 1, the planar shape in thesurface A of the n-side electrode 101 can be the shape indicated by thedotted lines. In this case, the light absorption by the reflection inthe electrode part can be reduced by reducing the electrode area and itis possible to further suppress the decrease in luminous efficiency bythe light absorption in parts other than the light-emitting layer. Astructure in which the p-side electrode has the shape of a comb and astructure in which both the n-side electrode and the p-side electrodehave the shape of a comb may also be adopted, and the same effect can beobtained in these cases.

Although in the above-described embodiments, GaN is used as thesubstrate, other substrates, such as a sapphire substrate and an SiCsubstrate, may be used. An electrode on the substrate side in thesecases is formed so as to be in contact with a conductive substrate orlaminated layer. For example, in the case of a sapphire substrate,because the substrate has insulating properties, it is possible to adopta structure in which the electrode is in contact with a conductivesemiconductor layer laminated on the substrate. It is also possible toadopt a structure in which the electrode extends from an insulatingsubstrate to a conductive semiconductor layer, and in this case, it ispossible to improve heat dissipating properties.

The present invention is not limited to the above-described embodimentsas they are, and in the case of implementing the present invention, itis possible to modify and substantiate the constituents of the presentinvention in a range of not departing from the gist of the invention.Also, it is possible to realize various inventions by properly combining

the multiple constituent elements disclosed in the above-describedembodiments. For example, some constituent elements may be eliminatedfrom all the constituent elements shown in the embodiments. Furthermore,constituent elements which cover different embodiments may bearbitrarily combined.

1. A semiconductor light-emitting element, comprising: a laminatedsection which has an active layer made of a semiconductor, and first andsecond clad layers each being disposed to sandwich the active layer andmade of a semiconductor; a pair of first high-reflection layers eachbeing disposed to sandwich the active layer in a first directionorthogonal to the laminated direction of the laminated section, whichhave high reflectance relative to a light emitted by the active layer;and a low-reflection layer and a second high-reflection layer each beingdisposed to sandwich the active layer in a second direction orthogonalto the laminated direction and crossing to the first direction, whichhave low reflectance and high reflectance respectively relative to thelight emitted by the active layer.
 2. The semiconductor light-emittingelement according to claim 1, wherein the second direction is orthogonalto the first direction.
 3. The semiconductor light-emitting elementaccording to claim 1, wherein a sectional area of the active layer in aplane orthogonal to the second direction is larger than the sectionalarea of the active layer in a plane orthogonal to the first direction.4. The semiconductor light-emitting element according to claim 1,wherein the laminated section has a shape in which a length of thelaminated direction is longer than a length in the first direction and alength in the second direction.
 5. The semiconductor light-emittingelement according to claim 1, wherein the first and second clad layersinclude a pair of third high-reflection layers which have highreflectance relative to the light emitted by the active layer.
 6. Thesemiconductor light-emitting element according to claim 1, wherein highreflectance of the first and second high-reflection layers are 80% ormore relative to the light emitted by the active layer.
 7. Thesemiconductor light-emitting element according to claim 1, whereinreflectance of the low-reflection layer is 10% or less relative to thelight emitted by the active layer.
 8. The semiconductor light-emittingelement according to claim 1, wherein the laminated section has firstand second contact layers which are formed on opposite sides of thefirst and second clad layers from the active layer, first and secondelectrodes being provided to supply a current to the active layer viathe first and second contact layers, and at least one of the first andsecond electrodes being contacted with a surface parallel to thelaminated direction of the laminated section at least one of the firstand second contact layers.
 9. The semiconductor light-emitting elementaccording to claim 1, wherein at least a portion of a side surface ofthe active layer is covered with a nitride-based insulator.
 10. Thesemiconductor light-emitting element according to claim 9, wherein thenitride-based insulator is a silicon nitride.
 11. The semiconductorlight-emitting element according to claim 1, wherein the active layer ismade of a nitride-based compound semiconductor.
 12. A light-emittingdevice, comprising: a mount substrate which has a heat sink; and asemiconductor light-emitting element mounted on the heat sink, thesemiconductor light-emitting element comprising: a laminated sectionwhich has an active layer made of a semiconductor, and first and secondclad layers each being disposed to sandwich the active layer and made ofa semiconductor; a pair of first high-reflection layers each beingdisposed to sandwich the active layer in a first direction orthogonal tothe laminated direction of the laminated section, which have highreflectance relative to a light emitted by the active layer; and alow-reflection layer and a second high-reflection layer each beingdisposed to sandwich the active layer in a second direction orthogonalto the laminated direction and crossing to the first direction, whichhave low reflectance and high reflectance respectively relative to thelight emitted by the active layer, the laminated direction of thelaminated section being in parallel to a surface of the heat sink onwhich the semiconductor light-emitting element is disposed.
 13. Thelight-emitting device according to claim 12, further comprising afluorescent material formed around the active layer of the semiconductorlight-emitting element.
 14. The light-emitting device according to claim12, further comprising a light guiding plate, a reflection plate or adiffusion plate disposed around the active layer of the semiconductorlight-emitting element.
 15. The light-emitting device according to claim12, wherein a sectional area of the active layer in a plane orthogonalto the second direction is larger than the sectional area of the activelayer in a plane orthogonal to the first direction.
 16. Thelight-emitting device according to claim 12, wherein the laminatedsection has a shape in which a length of the laminated direction islonger than a length in the first direction and a length in the seconddirection.
 17. The light-emitting device according to claim 12, whereinthe first and second clad layers include a pair of third high-reflectionlayers which have high reflectance relative to the light emitted by theactive layer.
 18. The light-emitting device according to claim 12,wherein the laminated section has first and second contact layers whichare formed on opposite sides of the first and second clad layers fromthe active layer, first and second electrodes being provided to supply acurrent to the active layer via the first and second contact layers, andat least one of the first and second electrodes being contacted with asurface parallel to the laminated direction of the laminated section atleast one of the first and second contact layers.
 19. The light-emittingdevice according to claim 12, wherein at least a portion of a sidesurface of the active layer is covered with a nitride-based insulator.